Optimizing Speed Controllers

[flameout]

Originally Posted by Ether

The output is always a "duty cycle" (PWM).

Perhaps what you meant is the difference between voltage mode and %Vbus mode...

Sorry I wasn't clear... that's what I meant.

To those not familiar with motor controllers (and the Jaguars in particular), the %Vbus (EDIT: Correction below) mode changes the duty cycle as a function of the Jaguar's input voltage so as to produce an output that simulates the specified voltage. The formula is as follows:

duty cycle = Target voltage
              Input voltage

The result of this formula should be scaled to [-1,1]. If scaling is required, then the requested voltage is not achievable unless the voltage of the Jaguar's power supply is increased. If percentage is required, multiply by 100%.

With brushed DC motors (I'm sure there are other motor types as well, but BLDC (EDIT: correction below) motors are all that FRC teams need to be concerned with), changing the duty cycle this way has exactly the same effect on the motor's outputs as giving it exactly the specified voltage would.

EDIT: As highlighted below by Ether, the Jaguar's voltage-control mode is it's "voltage" mode, not "%Vbus" mode.

Also, when I said "BLDC", I should have said "brushed DC".